Recent work has shown that the forebrain, in particular the hippocampus, exhibits high expression of aromatase (the 17-estradiol (E2) synthesis enzyme) in both males and females, and has significant E2- generating capacity. Under basal conditions, aromatase is highly expressed in neurons, whereas after brain injury, aromatase becomes highly expressed in reactive astrocytes. Currently, the roles and functions of local-derived E2 in the forebrain are poorly understood. The objective of this proposal is to elucidate the role of brain-derived E2 in both physiological and pathological situations. Our central hypothesis is that local E2 acts as a neuromodulator to regulate brain plasticity and function, and to help protect and repair the brain following injury. We will test the hypothesis utilizing novel mouse models with selective knockout of aromatase expression in forebrain neurons (FBN-ARKO-/-) or in astrocytes (AS-ARKO-/-) and by using a double neuron/astrocyte aromatase knockout (DB-ARKO-/-) mouse model. Aim 1 will determine the role of local E2 in regulating synaptic plasticity, neuronal communication, and behavior in the non-injured brain. We will determine whether loss of forebrain neuronal and/or astrocyte-specific E2 affects hippocampal synaptic plasticity, neurological reflexes, motor function activity, sensorimotor gating, anxiety, depressive- behavior, contextual fear, and cognitive function. Aim 2 will define the role of local E2 in modulating neuroinflammation, neuroprotection and repair in the injured brain. We will determine whether loss of forebrain neuronal and/or astrocyte-specific aromatase affects ischemia-induced neuronal loss, neurogenesis, gliosis, neuroinflammation, plasticity, and functional outcome. Aim 3 will elucidate the molecular mechanisms that mediate the actions and control of local E2 in the brain. We will determine whether loss of forebrain neuronal and/or astrocyte-specific E2 affects activation of membrane-initiated signaling pathways that promote neurotrophic and prosurvival effects (ERK, AKT, CREB), or prodeath and proinflammatory effects (JNK/P38MAPK) - key signaling pathways that are known to be regulated by extranuclear estrogen receptors (ER). At the genomic level, RNA-Seq will be used to profile gene expression differences in WT vs. KO mouse forebrains. Additionally, a potential key role of local E2 in control of the major neurotrophic factor, BDNF will also be examined. We will also determine the ability of extranuclear ER activators to rescue molecular and functional phenotypes observed in the ARKO-/- mice. Finally, the role of pro-inflammatory cytokines and the transcription factor C/EBP in the control of local E2 induction after GCI will also be examined. The proposed research is innovative due to utilization of novel mouse models that will define the role of brain-derived E2 in the brain. The studies will have a significant impact upon the field by elucidating the roles, mechanisms and control of brain-derived E2, which could lead to new ideas and new directions for the field, and to generation of potential new therapies for neurological disorders.